Within the next seven years, India will overtake China to become the world's most populous country. In just a year or two after that, once China's population has hit around 1441.5 million people, its population will start to decline for the first time ever.

India, meanwhile, will continue to grow until 2061 or so and only start to decline when its population has gone well past 1678.7 million people, when it will be the most populous country the world has ever seen.

2. Young, but not for long

By that point, we will be a significantly greyer country; India's median age will have crossed 40 by the time its population finally starts declining. The median age today is under 27 years.

3. The beginning of the end of the demographic dividend

By 2040 or so, India's demographic dividend will be conclusively over. Being a relatively young country, India has a low dependency ratio -- the ratio of children and the elderly to the working age population. Once fertility began to slow down, the dependency ratio began to fall from the 1970s and the share of the working population in the total population grew, becoming a huge potential strength for India. But as the population greys, India's dependency ratio will rise again, and that change becomes evident by 2040 or so. So if India wants to use its global competitive advantage in having a large working age population, it has around 20 years to do this.

4. Moms are younger, not older

Perhaps the most significant demographic change is the falling number of children every family in India is having -- the total fertility rate is already down to 2.3 children for every woman, and is expected to reach the replacement fertility rate (the number of children required to simply replace the existing population without it growing) of 2.1 by 2025.

Most people commonly believe that having fewer children and being better educated means that women are having their children later than ever, and hence the mean age at child-bearing should be falling in India. However what's actually happening is the opposite. The age at which a woman has her first child is indeed going up. But women are having fewer children not so much by having them later, but by still having them relatively early, and then stopping having them -- no more having your fifth and sixth child well into your 40s for Indian women. So, counter-intuitively, the mean age at childbirth -- the average age at which a woman has all of her children -- is actually falling in India.

That finally changes around 2025, when women start to have children later, and the mean age at childbirth starts to rise.

5. The sex ratio will finally improve

Sometime around now, India's sex ratio is projected to finally start improving. After 2020, India's sex ratio at birth -- the number of male births for every female birth -- is projected to finally start declining. Just a handful of countries have a worse sex ratio at birth as of 2015-2020, such as China, Armenia and Azerbaijan.

Another important change that is taking place right now -- the inexplicably high number of baby girls dying before they reach the age of five is slowing down, and male and female child mortality is falling and is at similar rates now.